A specific assay for elastin biosynthesis will be developed for use with elastin producing cells and tissues of pulmonary origin both in vivo and in vitro. The assay should replace existing methods which depend on the crosslinking of newly synthesized elastin and are thus relatively insensitive to variation in the rate of synthesis of noncrosslinked soluble precursor elastin (tropoelastin). This should also be more sensitive and specific than assays involving selective extraction of tropoelastin. The method is based on the extreme abundance (greater than 6 percent) of the amino acid doublet valylproline in elastin and its scarcity (0-0.5 percent) in other proteins. Alkaline hydrolysis or limited acid hydrolysis releases this doublet sequence quantitatively from polypeptide chains. Incubation of lung slices from young mice and rats with C14-valine will be followed by direct hydrolysis of the bulk tissue. Radioactive valylproline will be purified on a standard amino acid analyzer where it elutes as a well-defined peak in a clear region after phenylalanine. Split stream analysis (ninhydrin and scintillation counting) will provide quantitative data on the amount of valylproline. An elastin synthesis parameter will be derived from the ratio C14-valylproline/total protein, and the specificity of the assay will be compared for elastin-rich tissues (lung, aorta) and elastin-deficient tissues (liver, brain). Kinetics of tropoelastin synthesis in lung slices in vitro, and by whole lung in vivo, will be compared with in vivo rates of formation of crosslinked mature elastin (C14-lysine appearance in desmosine and isodesmosine). The assay will eventually be applied to cultured human lung fibroblasts (WI-38) and other pulmonary cell types to establish the cellular origin of elastin and to identify the factors (age, growth rate, nutrition, etc.) which control elastin biosynthesis.